Uranium pinhole collimators for positron emission SPECT imaging of small volumes

Depleted uranium (DU) pinhole collimators are evaluated for small volume SPECT imaging of 511 keV gammas from F-18 positrons, with a view towards small animal imaging. Tungsten (W) pinholes are examined for comparison. Line source measurements show FWHM as low as 6.5 mm for a 1 mm pinhole, and SPECT system FWHM of 5.2 mm at 39 mm ROR, and 6.3 mm at 69 mm ROR. Planar FWHM is smaller for DU than for W pinholes but is insensitive to aperture size for 1-3 mm dia. pinholes. These trends indicate penetration at pinhole edges, as confirmed by LSF shape. In test scans, neither DU nor W pinholes were able to resolve cold rods as large as 4.7 mm (diameter=2 X center-to-center spacing). U pinholes resolve 3.9 mm hot rods, imaging either F-18 alone or imaging F-18 simultaneously with Tc-99m. (Tc-99m scans, either alone or with FDG, resolved 2.3 mm rods.) DU pinhole SPECT currently shows poorer spatial resolution than high-resolution PET, but is open to improvements, and is capable of multiple-isotope acquisitions.